1. Field of Invention
The field of the current invention relates to methods of producing reactive laminated particles, and more particularly to mechanical methods of producing reactive laminated particles and the reactive laminated particles and products incorporating the reactive laminated particles.
2. Discussion of Related Art
Materials that react exothermically in controllable and predictable ways are desirable for many energetic applications such as: pyrotechnics, heaters, delays, munitions, explosives and propulsion, for example. In addition, increases in long-term stability, improvements in the rate and energy of reactions, and the ability to control and tune the rates and energies of reactions are also desirable for many applications.
In order to increase the reactivity of particulate systems, researchers in the past have developed powders or particles with nanometer scale diameters or dimensions. While more reactive, these powdered particles have been known to suffer from surface contamination, agglomeration in larger particles, non-uniform distributions of reactants and densities in multi-powder compacts, variability in particle size, and chemical instability.
Other methods to form reactive particles have involved forming core/shell particles. However, the resulting particles typically have only two to three shells or layers and thus are very small and very hard to manipulate if the reactant spacing (shell thickness) is only tens of nanometers thick. For ease of handling, it is desirable to use reactive particles with geometries that range in thickness, width, length or diameter from a few microns to several hundred microns, and reactive particles with geometries that enable packing or volume fractions ranging from 5% to almost 70%.
A different class of energetic materials, known as reactive multilayer foils and energetic nanolaminates comprising alternating layers of materials with large negative heats of mixing, has largely overcome many of the shortcomings of reactive powders and particles by enabling tuning and control of specific reactant chemistries that enable desired levels of stored energy and specific reactant spacing within the particles that enables a desired ignition threshold. In particular, the various design choices available for layer materials, layer dimensions, overall dimensions, bilayer periodicity, etc. enable such reactive multilayer foils and energetic nanolaminates to be particularly tuned and controlled.
Reactive laminate particles or powders can be fabricated by physical vapor deposition methods as described in our previous provisional patent (T. P. Weihs, G. Fritz, R. Knepper, J. Grzyb, A. Gash, J. Sze, Layered Reactive Particles with Controllable Geometries, Energies and Reactivities and Methods of Making the Same, U.S. Provisional Patent Application No. 61/107,915, filed Oct. 23, 2008; and U.S. application Ser. No. 12/605,281, filed Oct. 23, 2009), the entire contents of both of which are incorporated herein by reference. However, such fabrication methods can be expensive and alternative methods for low-cost, large volume fabrication of reactive laminate particles are desired for many applications.
Physical vapor deposition (PVD) of laminate reactive materials provides excellent control of chemistry, total thickness, and reactant spacing and thus is used for making thin films and foils (T. W. Barbee, Jr. and T. P. Weihs, Ignitable, Heterogeneous, Stratified Structures for the Propagation of an Internal Exothermic, Chemical Reaction along an Expanding Wavefront, U.S. Pat. No. 5,538,795, Jul. 23, 1996; T. W. Barbee, Jr. and T. P. Weihs, Method for Fabricating an Ignitable, Heterogeneous, Stratified Structure, U.S. Pat. No. 5,547,715, Aug. 20, 1996; T. P. Weihs, O. M. Knio, M. Reiss, D. Van Heerden, Method of Making and Using Free Standing Reactive Multilayer Foils, U.S. Pat. No. 6,991,856, Jan. 31, 2006). However, fabrication of bulk laminate materials by PVD is costly and very challenging. The cost can even be higher for making thick films (>100 μm). The high cost of fabrication can be attributed in part to the poor material utilization during PVD and the high capital costs of the deposition systems.
Mechanical fabrication of reactive materials (e.g., by rolling, forging and/or swaging) is a low cost method of making laminate reactive sheets and rods and thus very attractive (M. E. Reiss and T. P. Weihs, Method of Making Reactive Multilayer Foil and Resulting Product, U.S. Pat. No. 6,534,194, Mar. 18, 2003; Y. Xun, D. Lunking, E. Besnoin, D. Van Heerden, T. P. Weihs, O. M. Knio, Methods of Making Reactive Composite Materials and Resulting Products Thereof, U.S. Patent Application No. 2009/0178741, the entire contents of which are incorporated herein by reference). Material utilization is far better than PVD, material costs are low, and fabrication equipment is relatively inexpensive. However, when most reactive materials are rolled or swaged extensively to fabricate reactive materials with fine reactant spacing, the reactive materials often contain excessive cracking. These cracks can be both microcracks and macrocracks. The presence of cracks can lead to unwanted variability in material properties. Once initiated, self-propagating exothermic reactions can quench when the reaction front hits a large crack. The cracks can also lower the toughness of the samples, and their strengths and their ductilities can be very low, making handling and machining of the samples difficult.
For joining and sealing applications (soldering and brazing), energetic applications (reactive shells, fragments, pyrotechnic or other components) and heating applications (gas generators, thermal batteries) one often requires reactive materials in complex geometries such as patterned sheets or foils, curved sheets or foils, plates or rods with holes or open interiors, spherical or elliptical shapes, or nonuniform geometries.
One can pattern PVD films or foils via punching, etching or lift-off techniques. However, significant amounts of the sheet or foil can be wasted in some cases and one is often limited to planar geometries. One can form curved foils with PVD but fabricating thick curved sheets is challenging. Fabricating thin or thick sheets with complex curvatures is very challenging.
One can form rods, sheets or plates by swaging, rolling or even PVD and holes or patterns can be machined into these components but one wastes reactive material by doing so and the complexity that can be obtained is limited. Reactive materials with thick, nonuniform geometries are very difficult to fabricate by PVD of films and foils or by mechanical processing of rods, sheets or plates.
There thus remains the need for improved reactive materials and methods of producing reactive materials and products that incorporate the reactive materials.